U.S. Pat. Nos. 3,595,786 and 4,338,191 disclose feeder devices comprising a dissolution chamber having a liquid-inlet and outlet, the liquid passing through this chamber thereby contacting a tableted treating agent stacked within cylinders with lateral openings exposing the treating agent to the liquid. An adjustable weir is arranged downstream of the cylinders, causing a certain degree of damming of the liquid within the dissolution chamber.
This adjustable weir is designed to provide an adjustable height of the liquid level within the dissolution chamber at a given flow rate and the concentration of the treating agent in the effluent liquid may be adjusted by positioning of the cylinders. At different flow rates the height of the liquid level in the dissolution chamber is obviously different, and the above patents contain no teaching how a proportional relationship between the flow rate and the amount of treating agent dissolved in the liquid may be established. Feeders such as disclosed in the above patents do not provide a constant concentration of treating agent in the treated liquid under varying flow rates of the liquid.
U.S. Pat. No. 4,117,560 discloses an apparatus for treating fluids in a closed circuit with treating agent comprising a chamber receiving the fluid flow, wherein holding means for the treating agent are provided permitting contact between the passing fluid and the treating agent during the passage of the liquid through the above mentioned chamber.
This apparatus comprises further a combination of an underflow weir and an overflow weir upstream from the holding means which combination of weirs has the purpose of inhibiting the entrance of floating and sedimented solids into the treating chamber. This weir combination does not control the liquid flow through the treating chamber and thus does not influence the dissolution rate of the treating agent in proportion to the flow rate.
U.S. Pat. No. 3,495,948 describes a bypass dissolver comprising two main chambers, one receiving a larger, untreated flow portion and the other one a minor flow portion wherein treating agent is dissolved during its passage in contact with a pervious magazine of treating agent.
This feeder is designed such that the flow rate of the smaller stream portion, in which the treating agent is dissolved, remains constant irrespective of the flow rate in the larger stream portion or the total flow rate. Thus, the dissolution rate of the treating agent is constant over time, independent of the total flow rate.
A feeder according to the above patent, therefore, does not provide constant concentration of the treating agent in the effluent liquid but only a timewise constant supply thereof in a liquid of varying flow rate.
U.S. Pat. No. 3,746,170 discloses a liquid-treating apparatus having a tank, wherein the liquid to be treated is kept at a constant level and containers with treating agent are immersed into said liquid at an adjustable immersion depth. Manual adjustment of these containers to control the immersion depth is required. A constant concentration of treating agent in the liquid passing through this apparatus may not be obtained therewith.